A surface acoustic wave (SAW) device is an electro-mechanical conversion element that utilizes a surface wave propagating across a surface of body to convey energy between electrodes of an inter-digital transducer. When an electric signal is supplied to one of the electrodes, the body is stressed, and the stress becomes a surface acoustic wave. The wave propagates on the body and causes generation of an electric signal at the other transducer.
SAW devices are utilized in a wide range of applications. One example application is as a filter adapted for high energy transmission. Another example application is as a resonator in which a surface wave of large amplitude is present as a standing wave.
Current SAW devices may develop issues concerning hillocks, voids, or the like due to metal migration that takes place within aluminum metallized electrodes. The migration is due primarily to the induced stress. Such issues may readily occur for a SAW device that has very fine inter-digit fingers that provide the electrode transducer. Under such circumstances, the SAW device may experience deviation or shift away from desired frequency performance.
A SAW device that is utilized as an antenna duplexer (e.g., within a cellular handset) must be able to withstand a continuous wave with a high power input within a high frequency region. Specifically, the metallization of the inter-digit transducer, and also the metallization of the bond pads and busbars, must be able to withstand such use without undue degradation of performance.
Metallization systems for SAW amplifier duplexers have been developed for use within the 800–900 MHz frequency band. Also, some SAW antenna duplexer devices have been developed for the 1.8 to 2.1 GHz frequency band. In order to provide sufficient durability of such SAW antenna duplexers, there have been many attempts directed toward improvement. Specifically, the attempts have been directed toward improved power durability. Some of the efforts have been directed toward developing new compositions of aluminum alloy.
Generally, pure aluminum metal exhibits a poor antimigration property (i.e., subject to easy migration). Some of the previous work toward improvement has found that small amounts of dopant, such as Cu, Pd, Y, Sc, or Mg, have provided increased power durability. For small amounts of such dopant, device lifetime is increased. However, at a certain point, increases in the dopant amount causes an undesirable increase in electrical resistance. Thus, these related factors cause a balance between the increased lifetime and the increased electrical resistivity.